Prior art workers have devised many types of fastener driving tools. As used herein and in the claims, the term "fastener" is to be considered in the broadest sense, referring to substantially any fastener capable of being driven into a work piece. Examples of such fasteners are nails, staples and clamp nails of the general type taught, for example, in U.S. Pat. No. 4,058,047.
Perhaps the most common form of fastener driving tool is a pneumatically actuated tool. Prior art workers have developed a multiplicity of pneumatically actuated fastener driving tools to a high degree of safety and sophistication, of which the tool taught in U.S. Pat. No. 3,964,659 is exemplary.
More recently, there has been considerable interest in electro-mechanical fastener driving tools utilizing a solenoid mechanism or a flywheel mechanism to drive the fasteners. Electro-mechanical fastener driving tools are of particular interest for home use and industrial use where a source of compressed air is not available. An example of such a tool is set forth in U.S. Pat. No. 4,298,072.
The fastener driving tools thus far described are of the single blow variety, wherein the fastener is driven home by a single impact of the tool driver. Such tools are well adapted for industrial use, but they tend to be large, bulky and heavy and, therefore, are not as well suited for home use or the like. Such high powered, single blow tools, if misused, are capable of firing a fastener a considerable distance with substantial force. Furthermore, they tend to be noisy, complex in structure and expensive to manufacture.
As a result of the above, prior art workers, with an eye to light industrial applications and home uses, have also turned their attention to multiple impact fastener driving tools wherein simple rotary motion, obtained from an appropriate prime mover, is converted to linear reciprocating motion of a driving piece. Such tools have a number of advantages. First of all, they can employ a low power prime mover. As a result of the reduced power that must be dissipated, as compared to single blow tools, the multiple blow tools are characterized by reduced sound levels. Additionally, they are inherently safer than the single blow tools, since they are incapable of inadvertently firing a fastener over a considerable distance with substantial force. Finally, such tools can be of less complex, more compact, and lighter weight construction than the usual single blow tool.
Despite these advantages, applicants are unaware to date of any successful, large scale commercialization of such a multiple impact tool. Essentially, regardless of the type of fastener driving tool, fasteners are driven with a two-part system--force and velocity. It is well known that the higher the velocity, the easier it is to drive a fastener. It is believed that one of the primary difficulties encountered by prior art multiple impact tools was the fact that they did not produce high velocity impacts.
Generally speaking, prior art multiple impact tools have fallen into two basic categories. The first encompasses those tools which accomplish translation of rotary motion to reciprocating motion through the use of some form of eccentric or crankshaft. An example of such a tool is taught in U.S. Pat. No. 3,042,924. The second includes those multiple impact tools which employ some form of cam profile for translation of rotary motion to reciprocating motion. Exemplary tools of this nature are taught in U.S. Pat. No. 3,366,302.
The tools of the prior art which translate rotary motion into reciprocating motion through the use of an eccentric or crankshaft, produce a motion/velocity curve which can best be expressed as a sine wave. Thus, the fastener drive cycle produced by such a tool is initiated with zero velocity of reciprocation; reaches maximum velocity at the mid-point of the drive cycle; and terminates at zero velocity of reciprocation. Those tools employing an eccentric or crankshaft for motion translation accomplish the translation in a very smooth manner, but with a low and diminishing velocity.
Those prior art tools which translate rotary motion into reciprocating motion through the use of some form of cm profile, attempt to address this problem of attaining velocity in one of two ways. One method is to develop a cam profile which maximizes velocity to the point of reversal of the reciprocating motion. While this represents an improvement, once again such a tool produces the zero velocity condition at some point toward the end of its drive cycle. Furthermore, the motion translation achieved is not very smooth because of the need for rapid deceleration to effect the motion reversal. The other method employed by the prior art is to use a form of cam profile to precondition the drive cycle which is performed by some other power source than the rotating member. This additional power source is usually a spring of some type. These devices again represent an improvement over those devices discussed above, but they require an additional power source to perform the drive cycle and they necessitate an abrupt release by the cam of the other power source in order to release the drive power, and this produces high wear on the cam surface.
U.S. Pat. No. 3,015,244 illustrates an interesting approach wherein a tool includes a driver hammer element and an anvil member operated upon by the hammer element. The hammer element is connected to a prime mover drive shaft by means of a rubber-like cylinder. The cylinder is adapted to be placed in torsion to store energy. The rubber-like cylinder elongates when placed in torsion. This characteristic is utilized in causing the hammer element to be intermittently disengaged from and engaged with the anvil member.
The tool of the present invention utilizes rotary motion translated into reciprocating motion and, at the same time, overcomes the velocity problem which has plagued the prior art. The tool employs a prime mover to produce the necessary rotary motion and a driver to drive the fasteners. The translation mechanism employed by the tool comprises a flywheel for storing the rotary energy; an impact member either coupled to the flywheel or constituting an integral, one-piece part thereof and having at least one impacting surface; an energy transfer member which is free floating in the sense that it is not actively coupled to or constantly in engagement with the impact member, although it is engageable with the impact member; and a resilient energy absorber to arrest the energy transfer member at the termination of its drive cycle. The tool driver is engageable by the energy transfer member, or can be an integral, one-piece part thereof. The above recited elements produce relatively short (0.020-0.150 inch), high-velocity driver strokes in rapid succession to drive a fastener. Means are provided to normally bias the energy transfer member out of engagement with the impact member until the tool is pressed against the workpiece into which the fastener is to be driven. This action causes the energy transfer member to shift into the rotating path of the impact member.
The tool of the present invention is characterized by simple construction with a minimum of parts. The rotary energy is transferred to linear motion by impact, thereby producing a high-velocity transfer. The arresting means, which arrests the impact member and brings it to zero velocity to precondition the next cycle, is independent of the rotating elements. The mechanism of the tool of the present invention is not cycle-dependent. In other words, the tools of the prior art produce a drive cycle which is controlled by the rotating element. This is not the case with respect to the tool of the present invention. The drive cycle of the instant tool is dependent upon the force, provided by the operator, which causes the energy transfer member to engage the impacting surface of the impact member. If the operator applies no force during a revolution, no impact occurs, the energy transfer member being out of contact with the impact member. As a result of this, the operator can drive a fastener infinitely slowly, or as fast as he is willing to provide the force to engage the energy transfer member with the impact member. The motion translating mechanism of the tool of the present invention disengages when a fastener has been driven to the desired predetermined depth. Finally, the tool is compact, lightweight and relatively quiet in operation.